People said of Gilead that though it was a religious novel, you didn't have to be religious to enjoy it. You could bask in the elegy, and take or leave the theology. I don't think readers of Lila, Marilynne Robinson's third Gilead novel, have the same choice. Here, Robinson returns to the themes of her first novel Housekeeping: loss, transience, an ambivalence about home, a multivalent poetics of water. But here the waters are deeper, the currents stronger. What falls in is not lost but brought up from the depths, dripping and shining. In the end, nothing is ever really lost.

Here Robinson takes up the grander themes of redemption, judgment, and shame. Where the overwhelming quality of Gilead's narrative voice was radiance, here it's honesty, sometimes brutal, often beautiful. Lila's story unfolds in a kind of loose spiral where glimpses of the gravest things she's seen become gradually clearer. Race is the subtext of the first two novels, but here poverty and want, with their assault on dignity, are the background of Lila's life.

She grows up half wild, during the Depression, on the very edge of an already outcast tribe, raised by a woman whose courage and kindness hide beneath a savage ignorance. Her encounter with Reverend Ames and his entire tradition illuminates the Christian experience from the outside, and, though sweet at times, it can often seem glib. The church carries on its business of fellowship and casseroles, while throbbing hurts go untended. Theology is another language than the one Lila speaks, and yet she can read Ezekiel and find it utterly relevant. Robinson seems to be peeling off the layers of orthodoxy, and churchgoing, to find whatever yet lives within it. And she does find something living, something lovely, though it's bloodier and more wounded than picket-fenced churches show. Death and birth, blood and water, persist beneath the whitewash.

Of the cast of all three novels, Lila herself is probably the least religious, yet her story is the most profoundly spiritual. The plot turns on her salvation, in every sense of that laden word. She's retrieved from a perilous subsistence into the peace and safety of marriage with a respected preacher. She was lost and is found. But this never sits easily with her. She's never quite comfortable with the comfort she's offered. In this way the book asks what it means to be saved, or to be among the saved. At the same time it seems to say that nobody is ever ultimately lost. The people she's known - vagrants and drifters, mostly - though their lives seem utterly fragile and contingent, they persist somewhere, somehow. They outlive their contingencies. They are precious. And Lila can only accept her own savedness if they are saved too.

This is a very tender and profound vision of this perishing world: nothing can be kept, and nothing will be lost. One of Lila's questions is how life in this world is to be endured. But this final story also answers the longing question of Gilead: how can I leave all this behind? Holders of a different doctrine might quibble with this view of salvation for everybody and everything, but this is a portrait of God, refracted through a broken woman, that is full of a kind of raw glory, full of grace and truth. A God who seeks the lost, who reconciles to himself not just the saved but all things.

Gilead won a Pulitzer and Home won the Orange Prize. Lila has won the National Book Critics Circle award, but was overlooked by the Man Booker and other prestigious prizes. To my mind, though, it's the best book Robinson's written, and in time will be acknowledged as one of the truly great American novels.